Aerodynamic supplementary device for float aircraft

ABSTRACT

The additional device according to the invention for floats for seaplanes and floatplanes comprises four airtight bladders ( 10 ) to which compressed air can be applied, and which extend along the float and rest on side surfaces ( 11 ) of the float, which essentially consists of a box ( 1 ). The bladders ( 10 ) are composed of a flexible material with little expansion capability or an elastomer material, and are entirely covered with an elastic and watertight textile skin ( 9 ). In the state when compressed air is applied, the edges of the box ( 1 ), that is to say the side edges ( 8 ) and the keel edge ( 7 ), are smoothed. Thus, as soon as the aircraft has become airborne, the drag coefficient c D  of the float can be considerably reduced. The compressed air is released for the aircraft to land on and take off from water, so that the edges ( 7, 8 ) can produce their effect for directional stability (keel edge ( 7 )) and in order to prevent the Coanda effect (side edges  8 )).

The present invention relates to an additional device for seaplanes andfloatplanes according to the precharacterizing clause of Patent claim 1.Fluid-dynamic compromises have to be made with regard to the parts offlying boats, seaplanes, floatplanes and land aircraft provided withfloats which are located in the water during take-off and landing; inorder to avoid lengthy circumlocutions in each case, these parts will bereferred to as floats from now on. Said compromises are based on thefollowing considerations and requirements:

floats are intended to give the aircraft good directional stability onwater,

floats should be able to change easily from being pure buoyancy floatsto the sliding phase,

floats should have as little drag in air (c_(D)) as possible.

Technical measures which take account in particular of the firsttwo—hydrodynamic—requirements generally make the c_(D) value worse,while those which improve the c_(D) value generally destroy the buoyancyand sliding capability.

The Coanda effect (Henri Coanda 1886-1972) plays a central role here: onthe basis of the continuity law, water flows around curved surfaces on abody and, in the process, its speed is increased resulting, according toBernoulli's Law, in a pressure drop under water. Thus, if a float has adynamically advantageous shape, then this pressure drop results in itnormally being drawn into the water, rendering a sliding phase largelyimpossible, both during take-off and during landing on water.

In contrast, if a float is provided with, for example, a V-shaped lowersurface, with a sharp-edged transition into vertical walls, that is tosay with a sharp bilge edge, this not only improves the directionalstability, but also largely suppresses the Coanda effect. However, thisis invariably at the expense of the c_(D) being increased by severaltimes. The compromise to be reached between hydrodynamic and aerodynamicmaximization generally therefore needs to be made in favour ofhydrodynamics.

This applies in particular to the step or the step-shaped edge on thebottom of the float in virtually all known embodiments: this ishydrodynamically necessary in order to make the water flow turbulent andto allow air to flow in; however, it is aerodynamically disastrous sinceit likewise produces flow separation, but in this case this isundesirable.

The previously known attempts to overcome this poor compromise are notvery numerous:

either the edge—in plan view—is rounded at the rear

or an arrangement of moving flaps has been proposed which are extendedin flight and in the process cover the step-shaped edge, in order toimprove the aerodynamic aspect, for example in DE 38 41 878 A1.

The object of the present invention is now to provide a supplement forhydrodynamically optimized floats, which allows the c_(D) of such floatsto be improved to a major extent when the aircraft is airborne. Afurther object is to design such a supplement such that it is light andsuch that all the components which are subject to wear are easilyreplaceable. The way in which said object is achieved is described inthe characterizing part of claim 1, with regard to the main features ofthe invention, and in the following claims with regard to furtheradvantageous embodiments.

The attached drawing shows the idea of the invention with reference to anumber of exemplary embodiments. In the figures:

FIGS. 1a, b, c show three cross-sectional float shapes which are knownfrom the prior art,

FIG. 2 shows a side view of the known float from FIG. 1a,

FIG. 3 shows a first exemplary embodiment of a supplement according tothe invention with reference to FIG. 1a, in the form of a cross section,

FIG. 4 shows a second exemplary embodiment of a supplement according tothe invention with reference to FIG. 1a, in the form of a cross section,

FIG. 5 shows a third exemplary embodiment of a supplement according tothe invention with reference to FIG. 1c, in the form of a cross section,

FIG. 6 shows a fourth exemplary embodiment of a supplement according tothe invention with reference to FIG. 1a, in the form of a cross section,

FIG. 7 shows a fifth exemplary embodiment of a supplement according tothe invention with reference to FIG. 2, in the form of a longitudinalsection, and

FIG. 8 shows a plan view of the example in FIG. 7, from underneath.

FIGS. 1a,b,c show three floats in the form of a cross section, such asthose which are known as examples of the prior art.

FIG. 1a illustrates one frequently used profile: an essentiallyrectangular box 1 has an inverted roof-shaped profile 2 underneath; thetransition to the vertical is formed with a sharp edge, in order tosuppress the Coanda effect. The dashed line shows a round profile 3which is used as an alternative to the box 1 and which improves theaerodynamic characteristics.

FIG. 1b differs from FIG. 1a in that the roof-shaped profile 2 is in theform of a hollow keel 4, which results in improvements in terms of waterspray, directional stability and sliding characteristics, but obviously,in contrast, results in an aerodynamic deterioration. The dashed linesonce again show a variant 5 of the box 1 which tapers upwards.

FIG. 1c shows what is referred to as the Dornier profile, which has gooddirectional stability and sliding characteristics and is likewiseoptimized for water spray, but is regarded as being rather pooraerodynamically, because there are two edges 6 on each side.

The side view in FIG. 2 clearly shows an edge 12, which is alwaysprovided, irrespective of the choice of the cross-sectional profileshown in FIGS. 1a,b,c. As already indicated, the object of the edge 12is to cause flow separation in water, which is the only way in which theaircraft can lift itself off the water at all. However, it likewiseresults in flow separation in air, and this results in a greatlyincreased drag coefficient c_(D). Depending on whether the float underconsideration is the fuselage of a flying boat or the floats of aseaplane or floatplane, the c_(D) increase may be from 20% up to severaltimes that of the float under consideration. The idea of the inventionwill be explained in more detail with reference to a number of exemplaryembodiments, and based on FIGS. 3 to 8: virtually without exception, thefloats are nowadays manufactured from hard materials, such as metaland/or plastics. It is thus fundamental to the invention to provide asupplement which, if need be, be fitted retrospectively and is composedof pneumatic elements whose shape can be varied by applying compressedair and can be predetermined by material selection and cutting to size.

FIG. 3 shows a cross section of such a supplement according to theinvention, as can be fitted to a float as shown in FIG. 1a. Theroof-shaped profile 2 has two surfaces 11 and three edges 7, 8: one keeledge 7 and two side edges 8. The roof-shaped profile 2 is covered with atextile skin 9 which can expand, is coated such that it is watertightand is attached to the float in the region of the edges 7, 8. Flexiblebladders 10, running along the float, are inserted between the surfaces11 of the profile 2 and the textile skin 9, and can have compressed airapplied to them—via valves which are not shown here. The bottom of thefloat then assumes a curved shape, preferably a shape in which thesurface transitions between the bottom and the walls of the box 1 runsmoothly, and the transition from the rounded shape of one bladder 10 tothe other likewise runs smoothly. However, the side edges 8 are at leastweakened, both in their geometry and in their aerodynamic effect. Thiscan be achieved firstly by the flexible material from which the bladders10 are made being a textile material which has little expansioncapability and is coated such that it is airtight, and secondly by thebladders 10 being manufactured from an elastomer and the extent of thecurvature being set correctly in conjunction with the air pressure inthe bladders 10, on the one hand, and the stresses originating from theelasticities of the skin 9 and bladders 10. The first-mentioned varianthas the advantage that the desired shape is achieved above a specificair pressure; if the air pressure is increased further, the shape of thebladder 10 scarcely changes any further, provided the bladder 10 is, forexample, bonded to the surfaces 11 of the profile 2, at least in theregion of the edges 7, 8, over the entire length of the bladders 10.Different forms of connection in the form of a line or surface are, ofcourse, likewise included within the idea of the invention.

FIG. 4 shows a further embodiment of the idea of the invention. In thiscase, the float has four bladders 10 running over at least a majorproportion of its length. The construction, the material and theattachment of the bladders 10 correspond to what has been stated withregard to the bladders 10 in FIG. 3. The bladders 10 which areadditional to those shown in FIG. 3 rest on the side surfaces 11, whichlikewise have the number 11. The use of four bladders makes it possibleto produce smooth surface transitions over the edges 7, 8, with lessdeformation of the elastic skin 9. If a float with the variant 5 of thebox 1 illustrated in FIG. 1b is used, in which the side surfaces 11taper inwards in the upward direction and the surfaces 11 are in theform of hollow keels 4, then the exemplary embodiment shown in FIG. 4 ispreferred.

FIG. 5 illustrates an exemplary embodiment of the idea of the inventionwith a Dornier profile as shown in FIG. 1c. In this case as well, twobladders 10 can be provided, as shown, or else four as shown in FIG. 4.The essential features are the smooth transitions of the skin 9 over theedges, which are anotated by the number 6 here, or—as alreadystated—with them at least being weakened.

FIG. 6 illustrates a fourth exemplary embodiment of the idea of theinvention, in this case, by way of example, showing a cross-sectionalprofile corresponding to FIG. 1a. The longitudinally running bladders 10used here cover the two side surfaces 11 only partially: in each casefrom the side edge 8 to a longitudinal line 14 (which appears as a dothere). In this area, the bladders 10 are bonded to the side surfaces 11either over their complete area or else, for example, in the form of aline. The entire lower surface of the float, a cross section of which isillustrated here, is covered with the elastic textile skin 9. Whencompressed air is applied to the two bladders 10, the skin 9 now touchesthe float only in the areas of the keel edge 7 and of the side edges 8where it is also attached. Thus, with this exemplary embodiment, it ispossible to replace the side edges 8 by a smooth transition.

FIG. 7 is a detailed illustration of the transversely running edge 12shown in FIG. 2. This edge 12, followed in the aft direction by a step16, is required for hydrodynamic purposes since the water flow separateshere and allows the float to slide—both during the take-off and landingphases. Aerodynamically, that is to say as soon as the aircraft isairborne, the edge 12 has an extremely disturbing effect, as alreadystated. FIG. 7 thus illustrates how this disturbing effect is overcome,or at least considerably reduced, according to the invention: thesupplement according to the invention thus also includes an extension13, corresponding to the cross-sectional profile, of the edge 12. Whenthe bladder 10 is not inflated, the elastic skin 9 forces it essentiallybehind the extension 13 into the step 16. In this case as well, thebladder 10 is, of course, bonded to the float, for example, at leastalong the boundary of its contact surface with the float. In the statewhen compressed air is applied, it assumes the shape shown in FIG. 7,once again resulting in a smooth transition between the surface of thefloat forward of the edge 12 and that aft of it. The transition fromsaid surface to the skin 9 covered by the bladder 10 is also smooth.This prevents flow separation in the air flowing around the float.

The extension 13 of the edge 12 is preferably attached to the float bybonding, with the extension being appropriately shaped and prepared forthis purpose. Such bonding is, in contrast, prior art and therefore doesnot need to be described here. Depending on the configuration of thefloat, it may be advantageous to provide two bladders 10 filling thestep 16 rather than one bladder 10; for example when using a Dornierprofile.

FIG. 8 shows a plan view, from underneath, of the subject matter of FIG.7 using only one bladder 10. The dashed line shows, firstly, the edge 12which now projects from the extension 13 and, secondly, the boundary ofthe bonding of the bladder 10. If the aim is to fill only the step 16 bya bladder 10 with an elastic skin 9, the elastic skin 9 is drawn overthe bladder 10 to such an extent that a secure connection—for example bybonding—to the lower surface of the float can be produced, and then hasan edge 15. However, if it is also intended to carry out the smoothingof the other edges 6, 7, 8 according to the invention, the elastic skin9 preferably covers at least the entire lower surface of the float.

The lines for the compressed air are not shown, since they are known perse. They are preferably routed in the interior of the float.

In order to deflate the bladders 10 quickly, vacuum lines can also berouted to the bladders 10, so that they can be pumped out beforelanding. However, the lines which are used for the compressed air canalso be used for this purpose by providing valves which are known per seand provided a vacuum pump is present.

The supplement according to the invention may be of modular form, can bematched to the most usual types of and sizes of floats, may include onlythe smoothing of the edge 12, but may also include the smoothing of allthe edges 6, 7, 8.

Its use is particularly advantageous for floats on low-performanceaircraft such as light aircraft and ultralights, where the influence ofthe c_(D) values of the floats being improved in this way is noticeable.

What is claimed is:
 1. A pneumatic device adapted to be attached to afloat of an aircraft, the pneumatic device comprising: at least oneflexible airtight bladder arranged on the float, the at least oneflexible airtight bladder being adapted to have compressed air appliedthereto and comprising a flexible textile material having littleelasticity; at least one watertight elastic skin covering the at leastone flexible airtight bladder and bonded, at least in part, to thefloat; and wherein application of compressed air to the at least oneflexible airtight bladder causes smoothing of at least one surfacetransition in a region of at least one edge of the float that can leadto flow separation in the air.
 2. The pneumatic device of claim 1,wherein: the float comprises: a V-shaped profile cross section in a partthereof that enters the water; a keel edge; two side edges; and surfacesbetween the keel edge and the two side edges and adjacent thereto; andthe at least one flexible airtight bladder runs along the float, iscovered with the elastic textile skin, and rests on the surfaces.
 3. Thepneumatic device of claim 2, wherein the float has a bladder only onsurfaces located between the keel edge and at least one side edge of thetwo side edges.
 4. The pneumatic device of claim 3, wherein the at leastone bladder covers the entire surfaces.
 5. The pneumatic device of claim3, wherein the at least one bladder covers only a part of the surfacesadjacent to the side edges and is bounded by a line running along thesurfaces.
 6. The pneumatic device of claim 2, wherein the float has abladder both on surfaces located between the edges and on surfacesadjacent to the edges.
 7. The pneumatic device of claim 2, wherein theat least one bladder is arranged only forward of a transversely runningedge of the float.
 8. The pneumatic device of claim 2, wherein the atleast one bladder is arranged both forward of and aft of a transverselyrunning edge of the float.
 9. The pneumatic device of claim 1, wherein:the float has a Dornier profile cross section with four edges; the atleast one bladder: runs along the float; is covered with the watertightelastic skin; and is arranged such that the at least one bladder islocated between two edges of the four edges.
 10. The pneumatic device ofclaim 9, wherein the at least one bladder is arranged only forward of atransversely running edge of the float.
 11. The pneumatic device ofclaim 9, wherein at least one bladder of the at least one bladder isarranged forward of a transversely running edge of the float and atleast one bladder of the at least bladder is arranged aft of atransversely running edge of the float.
 12. The pneumatic device ofclaim 1, wherein: at least one bladder of the at least one bladder isprovided immediately aft of a transversely running edge of the float andis covered with the watertight elastic skin; the transversely runningedge has an extension projecting thereover and is attached to a forwardpart of the float; the at least one bladder of the at least one bladderis shaped and dimensioned such that, when compressed air is appliedthereto, the at least one bladder of the at least one bladder cancompensate for a step produced by the transversely running edge.
 13. Thepneumatic device of claim 1, wherein compressed air lines are provided,each of the at least one bladder being connected to a compressed airline.
 14. A The pneumatic device of claim 1, wherein the at least onebladder is adapted to be evacuated.
 15. The pneumatic device of claim14, wherein vacuum lines are provided and each of the at least onebladder is connected to a vacuum line.
 16. The pneumatic device of claim13, wherein vacuum lines are provided and each of the at least onebladder is connected to a vacuum line.
 17. The pneumatic device of claim16, wherein valves with a controller are provided and the compressed airlines and the vacuum lines are identical, the lines being operated bycontrolling the valves.
 18. The pneumatic device of claim 15, whereincompressed air lines are provided, each of the at least one bladderbeing connected to a compressed air line.
 19. The pneumatic device ofclaim 18, wherein valves with a controller are provided and thecompressed air lines and the vacuum lines are identical, the lines beingoperated by controlling the valves.